1. Field of the Invention
The present invention relates to a seasoning method for wood used as a building material of a structure or a component material of fittings.
2. Description of the Prior Art
The conventional wood seasoning method is roughly divided into natural seasoning and artificial seasoning. Artificial seasoning includes a seasoning method using a heat source of gas, electricity, or steam, a reduced-pressure seasoning method using heating or high frequency, and a dehumidification seasoning method.
Because natural seasoning is a method of putting green wood at a well-ventilated place to naturally season the wood, it requires a lot of seasoning days and has a disadvantage that the number of seasoning days cannot be determined because it is subject to weather. Moreover, the wood becomes heterogeneous because its moisture content cannot be kept constant and moreover, the wood cannot be seasoned up to a certain moisture content or less. Therefore, wood used is dried due to air conditioning in a room after built and resultingly, structures or fittings are deformed.
In the case of artificial seasoning, it is possible to decrease the number of seasoning days, specify the number of seasoning days, and obtain wood with a low moisture content, and comparatively small warps, cracks or deformation because this method is not influenced by weather. However, the costs for a heat source and equipment increase.
In the case of seasoning using gas or electricity as a heat source or using steam, temperature and humidity can easily be adjusted. However, the equipment cost and energy cost increase and problems lie in the durability of equipment including a furnace and machinery.
Reduced-pressure seasoning is performed by reducing pressure and thereby lowering the boiling point of water (approx. 41.degree. C.). When the seasoning temperature exceeds 80.degree. C., wood fiber is swelled and broken. In other words, strength deterioration occurs. In the case of this method, when the wood temperature lowers due to sudden seasoning, the seasoning speed decreases. Therefore, an effective seasoning time is up to approx. 2 hours. Moreover, because wood temperature unevenness occurs in stacked wood when the wood temperature rises and thereby, unevenness of moisture content occurs in finished wood.
In the case of dehumidification seasoning, equipment is simple and its operation is also easy. However, seasoning time increases.